Currently, communications based on electronics are being pushed to their limits due to ever-increasing demand for information processing and data transmission, and communications based on photonics are being intensely developed due to their high bandwidth and resultant extremely large information capacity. Limitations, however, exist with the photonic communications in terms of the high cost of critical waveguide devices such as modulators, switches, optical interconnects and splitters that are predominantly based on inorganic materials (e.g., silica, lithium niobate, and III-V semiconductors). The difficulties in processing and integrating these inorganic materials also limit the extensive application of wavelength multiplexing and demultiplexing. Therefore, innovations in novel passive waveguide materials that are cost effective, excellent in optical performances (e.g., high optical transparency, low birefringence, good material stability), readily processable, and can enable the integration with very scale semiconductor are being actively pursued.
Organic polymers represent promising candidates for waveguide devices1, due to their good processability, inexpensive mass production, and structure-property tunability. Various highly deuterated and halogenated polymers containing the minimum amount of absorptive bonds such as C—H, O—H, and N—H were established and their excellent waveguiding properties were studied2-5. However, for practical device applications, challenges still remain in developing polymers that have excellent comprehensive material properties such as good transparency and small birefringence, controlled refractive index, good thin-film forming ability, good material stability (birefringence relaxation and chemical and mechanical stability), and easy processability. Therefore, polymers with high glass transition temperatures and ability to cross-link either thermally or photochemically are highly desirable.
Poly(arylene ethers) which are well known high-performance polymers used in a wide range of demanding applications from aerospace to microelectronics, are characterized by their excellent thermal, mechanical and environmental stabilities, In addition, due to the existence of flexible ether linkages in the backbone, these polymers commonly have a low birefringence.3e,5 Because of these attractive properties, attention has been drawn to the highly fluorinated poly(arylene ethers) as optical waveguide materials.6,7 However, their application into photonic devices is limited. One of the reasons for this could come from the difficulties in obtaining structurally well-defined polymers using the traditional polycondensation reactions between the highly active decafluorodiphenyl monomers (i.e., decafluorodiphenyl ketone (DFPK) or decafluorodiphenyl sulfone (DFPSf)) and bisphenol compounds. To explore the potential of these types of polymers in waveguide applications, Ding et al. recently established an efficient synthetic method to the highly fluorinated, high molecular weight, linear fluorinated poly(arylene ether ketones) and poly(arylene ether sulfones) (FPAEKs and FPAESs). All the polymers showed good processability, high glass transition temperature, low optical loss at 1550 nm, and small birefringence.8,9 Encouraged by these studies, we have developed a systematic approach to the preparation of highly fluorinated FPAEKs and FPAESs waveguide materials that involves the introduction of cross-linking functionality and the fine-tuning of refractive indices of the polymers by the use of cross-linkable tetrafluorostyrol groups as pendant groups and bromo groups into polymer structure.